Kleptomania is repeated occurence where a person cannot resist the impluse to steal things, and when the reason for this is not economic or need of something for own usage. A person can get caught in kleptomania if he or she steals something, and finds that this reduces anxiety. There is then a risk that the same method is repeated, the next time the person has unbearable anxiety.
A cleptomaniac gets stimulation, satisfaction and release during the actual act of stealing, in the same way as a shopping addict gets a "kick" out of shopping. This kick is caused by stimulation of the pleasure centers in the brain from signal substances in the brain. If the kleptomaniac is down or stressed, then she may feel a compulsion to steal in order to counteract the anxiety. That this is so is shown by the fact that female kleptomaniacs steal more in the days immediately before menstruation. Kleptomania thus has many similarities to alcohol and drug abuse.
In psychotherapeutic treatment of kleptomania, the patient lies on a couch and is helped to get into contact with the inner tension that urges her to kleptomania. The therapist helps the patient to get into contact with her inner psychic pain, she is helped to find better ways of handling her anxiety, and she learns to handle her problems in more rational ways.
The kleptomaniac does not aim at gaining money by stealing. If she sells the stolen goods, this is probably not kleptomania at the time of selling, but may still be kleptomania at the time of stealing.
Your brother's wife needs professional help with her anxiety. People close to her should talk honestly and openly with her, and set limits for her, before the police do this.
I treat cleptomania with gestalt therapy. The patient gets in contact with her anxiety ande learn other ways of dealing with her emotion than stealing.